tensar glasgrid brochure
TRANSCRIPT
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PAVEMENTREINFORCEMENT SYSTEMS
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Fatigue and reflective cracking in pavements is typically caused
by traffic loading, age hardening or temperature cycling. When
cracking is present, the traditional remedy has been to apply
thicker asphalt overlays. For each inch of applied overlay,
existing reflective cracks are generally deterred from reaching
the surface for a period of one year.
THE GLASGRID SYSTEM EXTENDS PAVEMENT LIFE
BY UP TO 200%
The GlasGrid Pavement Reinforcement System provides
additional support to resist the migration of reflective cracks in
roadway applications. Manufactured by Saint-Gobain ADFORS
in Albion, New York, this interlayer system is composed of a
series of fiberglass strands coated with an elastomeric polymer
and formed into a grid structure. Each strand has a remarkably
high tensile strength and high modulus of elasticity; this isparticularly important as asphalt concrete typically cracks at low
strains. This combination makes the GlasGrid System stronger
than steel, pound for pound.
When the GlasGrid System is sandwiched between the
leveling and surface course asphalt in a conventional asphalt
overlay, it becomes the hidden strength in the road designed
to turn vertical crack stresses horizontally and effectively
dissipate them.
EASILY INSTALLED AND UP TO THE TASK
The GlasGrid System is easily installed without specialized
equipment or labor. With its pressure-activated adhesive, its
considered to be the most expedient interlayer system relative
to installation time. The GlasGrid System has proven to be
effective in every geographical area and climate from desert
environments to near-arctic conditions.
HIGHLY MILLABLE
In contrast with other interlayer systems, the GlasGrid Systemis easily broken up by traditional milling equipment. It also has
an additional benefit: its main component is silica, a natural
substance that is environmentally friendly.
The GlasGridSystem extends
pavement life thus reducing
maintenance and life cycle costs.
Todays Most Advanced Pavement Rehabilitation System
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How the GlasGridSystem Reinforces a Pavement
When conventional rehabilitation procedures are used,
an asphalt overlay is placed over the existing rigid or flexible
pavement. This provides some additional road life, but the
existing reflective cracks continue to propagate prematurely
toward the surface, as shown in Figure 1.
When used to reinforce asphalt concrete, the GlasGrid System
helps to create a composite material combining the compressive
strength of the asphalt mix with the tensile strength of glass
fibers. By introducing a stiff tensile element at the base of an
overlay, cracks propagating toward the surface are intercepted
and prevented from immediately migrating further. Instead,
the crack is redirected horizontally, as shown in Figure 2.
This process works best when through-hole bonding takes
place between the asphalt layers. As the term suggests, this
involves the development of a strong bond between the overlay
and the underlying level-up asphalt layer. This can be achieved
only when an open aperture grid structure is used for reinforce-
ment. The GlasGrid reinforced overlay will itself start to crack
in time, but at a much reduced rate, thereby significantly
extending the life of the road.
GlasGrid System
FIGURE 1: Cracks migrate toward surface in unreinforced overlay. FIGURE 2: Cracks are redirected in GlasGrid reinforced overlay.
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Engineers today can choose from several interlayer systems.
These systems are made from various asphalt binders in
combination with sand and/or aggregate, or from one or more
geosynthetics, which may also be combined with binders.
Bituminous-based interlayer systems such as slurries and seals
provide effective waterproofing but even with the advancement
in modified binders, they offer limited crack mitigation benefits.
Over the last 30 years, geosynthetic interlayers have proven
to be worthy alternatives with their added stiffness, uniform
quality and widespread availability.
As depicted in Figure 3, a number of criteria can be used
to determine the suitability of a specific interlayer product.
Researchers have found that the performance of a geosynthetic
interlayer system can be predicted based on the key material
properties structure and strength.
STRUCTURE
The interlayer system is defined as being either open (GlasGrid
System and steel mesh systems) or closed (composite grids andpaving fabrics). An open grid structure promotes through-hole
bonding (Figure 4) and more efficient stress transfer to the
grid by both the overlying and underlying aggregate matrices of
the asphalt layers. This is particularly important to prevent the
propagation of active cracks within the pavement. By contrast,
the transfer of crack stresses in fabric-based interlayer systems
takes place through the relatively weak bond formed between
the asphalt binder and the fabric.
STRENGTH
Only GlasGrid Mesh and steel mesh systems have sufficient
tensile strength at strains less than 3% to deter the propaga-
tion of cracks caused by traffic loading or thermal movement.
GlasGridSystems Performance Exceeds Other Interlayers
The GlasGridSystems open
grid structure promotes the
efficient transfer of stress from
both overlying and underlying
asphalt layers.
Wearing
course
GlasGrid
open grid system
Composite
grid fabric system
Binder
course
GlasGridsteel mesh
Compositegrids
glass-based
Pavingmats
Compositegrids
polyester-
based
Non-wovenfabrics
High
Thermal, Lane Widening or Block Cracks
Block or Flexural Cracks
Low
Low
High
Interlayer Strain Resistance
PotentialCrackReflectionActivity
FIGURE 3: Suitability of interlayer products for medium to hightraffic conditions.
FIGURE 4:Through-hole bonding occurs between the ribs in the open gridstructure of the GlasGrid System.
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CREEP
Long-term creep strength is required to restrain the propagation
of cracks associated with thermal movement or lane widening.
The GlasGrid System and steel mesh are the only grids that
possess sufficient creep characteristics to resist a high level
of sustained stress over long periods of time.
EASE OF INSTALLATION
With its pressure-activated adhesive, the GlasGrid System
is the fastest installed interlayer on the market. As much
as 25,000 square yards of grid can be installed in one day
using a standard laydown unit. In addition, the installation
of the GlasGrid System can be easily adapted to local weather
conditions or unique construction requirements.
MILLABILITY AND RECYCLABILITY
With the exception of steel grids in thin asphalt overlays, most
geosynthetic interlayer systems are millable using conventional
reclaiming equipment. However, when it comes to recycling
reinforced asphalt, only pavements reinforced with the GlasGrid
System can typically be ground up and reused in other roadprojects as a recycled asphalt pavement, or RAP (Image A).
PROVEN PERFORMANCE
Although advancements have been made to the coating and
adhesive, the GlasGrid System is still manufactured as it was
originally more than 20 years ago. This is testament to the
products extensive and proven success on project sites
throughout the world.
IMAGE A:Milled asphalt containing GlasGrid product can be easily recycledfor use on other projects.
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Research Quantifies the Benefits of the GlasGridSystem
The use of interlayers for reflective cracking has been extensively
researched over the last 30 years. In particular, three key
research projects have quantified the benefits of using GlasGrid
and help define its areas of application.
TEXAS A&M UNIVERSITY
Studies using the Overlay Test (Figure 6) and the Beam Fatigue
Test (Figure 7) on reinforced asphalt beams demonstrated
a two- to three-fold improvement in the life of a GlasGrid
reinforced overlay compared with an overlay constructed using
the same thickness of unreinforced asphalt. These two test
methods are still used widely to evaluate the performance
of asphalt mixes and interlayer systems.
A sub-study was also conducted to compare the performance of a
thinner reinforced section to a thicker unreinforced section. These
results are presented in Figure 5. These results show at least a
10-fold increase in the life of the thinner, reinforced asphalt.
In addition to the main laboratory testing undertaken at Texas
A&M University, a performance prediction model was developed
using the test data. Using traffic, temperature and pavement
geometry variables, comparisons were made of the predicted
performance for unreinforced and GlasGrid reinforced overlays.
For the example shown in Figure 8, the predicted performance
benefit of the 100 kN GlasGrid reinforced overlay is 1.5 to 2
times that for the unreinforced overlay. The performance of
a 200 kN product (GlasGrid 8502 or 8512) is expected to be
double that of the 100 kN grid.
FIGURE 7 FIGURE 8
FIGURE 6
X 2
X 2
X 2
1,500 days
1,000 days
500 days
30F 50F 70F
Temperaturedifferential
Unreinforced
Glasgridreinforced
7-in. thick overlay
Performance Prediction Results
Schematic Diagram of the Beam Fatigue Test
Schematic Diagram of the Overlay Test
15 in. (380 mm)
Fixedplate
Movableplate
Grid
in. (19 mm)
Grid
P P
RR
3 in. (75 mm) thick reinforced beams
4 in. (100 mm) thick unreinforced beams
(No. of Cycles to Failure)
Log(Strain)
10-2
10-3
10-4
10-5
1000 10,000 100,000 1,000,000
> 10 times
FIGURE 5: Simple Beam Test Results fora GlasGrid reinforced 3-in. thick beam
vs. a 4-in. thick unreinforced beam.
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THE UNIVERSITY OF NOTTINGHAM, UK
An interface bond test (Figure 9) was used to measure the
quality of the bond between various interlayers and the asphalt.
The test results shown in Table 1 strongly suggest that the
presence of a fabric and not grids results in a serious
reduction in the interface shear stiffness.Semi-continuously supported beam tests (Figure 7, on page 6),
were also conducted at the University of Nottingham to
determine the ability of interlayer materials to resist crack
propagation in notched asphalt beams. The test simulates a
stress distribution similar to that found in pavements under
normal trafficking conditions.
The results shown in Table 2 on page 10 present the worst
performing section (in this case the unreinforced section) and
apply a fatigue factor to the other sections in order to represent
the reduced rate of crack propagation. (i.e., the greater the
fatigue factor, the lower the crack propagation rate.)
The fatigue factor and bond strength associated with a particular
interlayer are key input parameters for the performance model
developed. Based on the data shown, the model predicts that a
GlasGrid interlayer will enhance the crack propagation resistance
for an asphalt overlay by a factor of two to three times.
DELFT UNIVERSITY, THE NETHERLANDS
Following an extensive field performance evaluation study
and comprehensive laboratory testing program, a performance
prediction model was developed for pavement overlays subject
to reflective cracking caused by thermally induced stresses. This
model was subsequently used to develop the Anti-Reflective
Cracking Design Software (ARCDESO) as detailed on page 9. It
also demonstrated that for a range of input parameters, the
design life of an asphalt overlay reinforced with the GlasGrid 8501
product is likely to be two times that for an unreinforced overlay.
Direction of load
application
Stiffener Epoxy Tie bar
Load cellRollers
Normal load
Interface
Specimen
Epoxy
o
h
FIGURE 9:Interface bond test apparatus
TABLE 1: Reported values of interface shear strength and stiffness completed at University of Nottingham, UK.
Geosyntheticinterlayer
Products Interface Shear Stiffness (MPa/mm) Interface Shear Strength (kPa)
Open Grid Type 1 24.7 (68%) Not failed
Composite Grid Type 1 8.1 (22%) 240
Composite Grid Type 2 14.3 (40%) 270
GlasGrid 36.4 (100%) Not failed
Composite Grid Type 3 14.1 (40%) 245
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NCAT TEST FACILITY, OPELIKA, ALABAMA
The National Center for Asphalt Technology (NCAT) features
one of the countrys largest and most advanced full-scalepavement testing facilities (Image B). During construction for
the Centers inaugural test sections in 2000, GlasGrid 8501
was included in a 100-foot long section of track. An adjacent
100 feet of unreinforced track served as a control section.
The entire track is supported by 20 in. of hot mix asphalt (HMA)
base to isolate distresses to the top four inches. The Marshall
SMA test mix consisted of a -in. nominal maximum aggregate
size, crushed granite and flyash mineral filler. A 6.2% SBR-modi-
fied PF76-22 liquid binder was specified. An emulsion tack coat of
type CSS-1h was applied at a rate of 0.03 gallons per square yard
before the placement of each lift of asphalt; the GlasGrid was
placed after the application of the tack coat on the binder course.
Both sections were subjected to 20 million Equivalent Single
Axle Loads (ESALs) of accelerated traffic loading, the equiva-
lent of 20 years worth of trafficking on a typical interstate
highway. Following this intense trafficking, longitudinal
cracking was observed throughout the length of the control
section. In contrast, no cracking was observed in the GlasGrid
reinforced test section. An exploratory core of the reinforced
section removed after trafficking showed that the GlasGrid
was still intact, bonded to both the underlying and overlying
layers of asphalt (Image C).
Research Confirms Benefits of the GlasGridSystem
IMAGE B: GlasGrid was installed at theNational Center for Asphalt Technology
(NCAT) pavement test track in Opelika, AL.
IMAGE C: GlasGrid remains intact after 20 million ESALsof traffic loading.
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The following software programs can be used for the design
of overlays incorporating the GlasGrid System. Tensar
International Corporation (Tensar) provides analyses of asphalt
overlays using these programs at no charge. For more informa-
tion, check with your local Tensar representative.
OLCRACK
The OLCRACK software was developed based on the results of
a study undertaken at the University of Nottingham in the UK.
Designs for GlasGrid reinforced overlays on flexible pavements
are based on traffic-induced stresses.
Design considerations include:
Anticipated traffic loading (magnitude and intensity)
Thickness and material properties of the existing
pavement structure and the new asphalt overlay
Width and spacing of cracks on the existing pavement
Subgrade material properties
A typical set of results from the OLCRACK software is shown
in Figures 11 and 12. In this example, the design life has been
increased from nearly 700,000 ESALs to more than 1.6 million
ESALs with GlasGrid reinforcement.
ANTI-REFLECTIVE CRACKING DESIGN SOFTWARE
(ARCDESO)
The ARCDESO software was developed based on the researchundertaken at Delft University in the Netherlands. The program
helps design unreinforced and GlasGrid reinforced overlays
constructed on flexible, semi-rigid and rigid pavements
subjected to thermally induced stresses.
Design considerations include:
Location of the project used to retrieve local
temperature data from any recognized local
or international weather database
Anticipated maintenance strategy (e.g., tack coat
and four-inch thick asphalt overlay)
Thickness and material properties of the existing
pavement structure
Width and spacing of cracks on the existing pavement
Subgrade material properties
Based on a discrete set of input data, the ARCDESO software
predicts the crack development rate for reinforced and
unreinforced overlays. A typical set of results is shown in
Figure 10 (above). In this example, GlasGrid reinforcement
more than triples (3x) the design life of the overlay.
Design of Reinforced Overlays
700,000 ESALs
1,600,000 ESALs
GlasGrid
10,000,000100,000
LevelinAsphalt
Number of wheel passes
1,000,000
Top-downBottom-up
Top-downBottom-up
70
60
50
40
30
20
10
70
60
50
40
30
20
10
FIGURE 11: Unreinforced crack development plot. FIGURE 12: Reinforced crack development plot.
10,000,000100,000
LevelinAsphalt
Number of wheel passes
1,000,000
FIGURE 10:Estimated life of GlasGridreinforced vs. unreinforced overlay for a
typical composite pavement structure.
100
90
80
70
60
50
40
30
20
10
0
Years
3.2 fold increase in life
%R
eflectedCracksper100m(
300ft)
0.0 3.5 7.0 10.5 14.0 17.5 21.0 24.5 28.0 31.5 35.0
Unreinforced
Reinforced withGlasGrid 8502
35.0
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0
Cost Benefits of the GlasGridSystem
100
60
4 years 5 years 10 years 12 years Time
Line A Line B
PavementConditionIndex(PCI) Predicted pavement condition as designed
based on structural analysis only
Pavement condition due to premature
propagation of reflective cracks
Predicted pavement condition based on
reflective crack control using GlasGrid
reinforcement
Hypothetical Plot of Pavement Deterioration Over Time
FIGURE 13
To determine the potential long-term cost benefits of
the GlasGrid System, it is first necessary to predict the
performance of a particular overlay.
In Figure 13, the continuing deterioration of a pavement
surface is indicated by a corresponding reduction in the
Pavement Condition Index (PCI). In this example, a four-inch
thick overlay for a high volume road has been designed to last
for 10 years. If there were no reflective cracks present on the
underlying pavement surface, the deterioration of the new
pavement would likely continue along the solid line shown.
Unfortunately, the existing pavement surface exhibits reflective
cracking. Therefore, although the four-inch thick asphalt overlay is
sufficient to last for 10 years from an overall structural perspective,
nearly all of the existing cracks will have propagated through the
new asphalt after approximately four years; this is based on thegeneral rule that reflective cracking propagates through an asphalt
layer at a rate of one inch per year.
As significant reflective cracking begins to appear at the
surface, the rate that water seeps into the pavement increases.
The pavement surface is predicted to deteriorate as indicated
by Line A in Figure 13. In this example, the pavement would
require a major rehabilitation after only five years as opposed
to the scheduled 10 years. At this point, the owner is faced with
a difficult situation and left with three principal options:
Scenario 1 Undertake a full rehabilitation of the
pavement by adding an additional four inches of asphalt.
Scenario 2 Do nothing and tolerate a poor quality road
for the remainder of its 10-year design life. At that
point, the existing road will likely require an additional
two inches of asphalt over and above the regular overlay
thickness for the pavement. This is necessary in order to
overcome structural deterioration resulting from its use
while in a poor condition.
Scenario 3 Close down the road for a major crack
sealing operation after five years. As this is more of apartial fix to the problem, it is likely that an additional
one-inch thickness of asphalt will be required over and
above the regular overlay thickness for the pavement
at the end of its design life.
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Interlayer Type
Interface BondStrength(MN/m2)
Fatigue Factor(decreased rate of crack propagation)
Mechanism(above/below interface)Above Interface Below Interface
GlasGrid 10 4 4Through-hole bonding
(THB)/THB
Composite Grid 0.1 4 1 THB/Adhesion
Fabric 0.1 1 1 Adhesion/Adhesion
Unreinforced 0.1 1 1 Adhesion
TABLE 2: Input parameters used to characterize reinforcement for performance prediction.
Cost Item Scenario 1 Scenario 2 Scenario 3 Scenario 4
Original 4 in. overlay $10/sq yd $10/sq yd $10/sq yd $10/sq yd
New 4 in. overlay after 5 years $10/sq yd
Inflation for new overlay $4/sq yd
Traffic accommodation(based on 25,000 AADT) $3/sq yd $3/sq yd
Crack sealing operation $3/sq yd
Extra thickness of AC at 10 years $5/sq yd
(extra 2 in.)
$2.50/sq yd
(extra 1 in.)
Inflation for extra AC thickness $4/sq yd $2/sq yd
Cost of GlasGrid $5/sq yd
Total Cost $27/sq yd $19/sq yd $20.50/sq yd $15/sq yd
TABLE 3:Approximate cost of the various rehabilitation scenarios and a reinforced pavement using full-width GlasGrid 8501and 8511 products.
A breakdown of the typical costs associated with each of these
scenarios are shown in Table 3.
Scenario 4 Excluding the initial cost of the four-inch
thick asphalt overlay, each of the additional costs
associated with the first three scenarios can be avoided.
Line B in Figure 13 illustrates that reflective cracking ofthe overlay is deterred until Year 12 if GlasGrid is initially
used. In this example, the GlasGrid System is predicted
to extend the crack resistance of the overlay by a
factor of three, allowing the road to reach the end
of its structural design life. This is described below
in Tables 2 and 3.
The bottom line: there is a significant cost advantage (2040%)
in this example to using the GlasGrid System in overlays
constructed over cracked pavements. These benefits will vary
depending upon local design conditions and material costs.
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Proven Performance
Unlike most other interlayer products, the GlasGrid System has
decades of proven performance. Thousands of successful projects
worldwide have utilized GlasGrid to retard the migration of reflective
cracks; examples of four such projects are detailed below.
U.S. HIGHWAY 96, LUMBERTON, TEXAS
This five-lane highway is one of the main arteries of Interstate 10
and links Beaumont, Texas with several smaller cities (Image D).
The road, originally constructed as a flexible pavement, is extens-
ively trafficked by commercial vehicles and heavy trucks. In 1993,
an annual average daily traffic (AADT) flow of 20,600 was recorded.
In order to reduce thermal and fatigue-related reflective cracking,
the Texas Department of Transportation approved the installation
of GlasGrid 8501 mesh over the entire width of a one-mile segment
in the area most affected by cracking. The grid was placed on top
of a 1.5-in. thick leveling course and covered with a 1.5-in. thick
HMAC Type C wearing course.
At each end of the test section, control sections constructed
without the GlasGrid System were monitored along with the
GlasGrid Reinforced Overlays for a period of six years. The results
are presented above in Figure 14. The sections of the road reinforced
with the GlasGrid System show a substantial improvement with
significantly fewer cracks reflected at the surface.
U.S. HIGHWAY 190, HAMMOND, LOUISIANA
U.S. Highway 190 is a secondary arterial road located between
Covington and Baton Rouge, Louisiana (Image E). It wasoriginally constructed as a rigid pavement. When rehabilitation
of the road took place in 1994, an AADT of 8,900 had been
recorded the previous year. However, the road originally carried
substantially more traffic prior to the construction of the local
segment of Interstate 12. As a result, a large number of
transverse and longitudinal cracks had developed in the
existing full-depth asphalt and composite pavements.
The Louisiana Department of Transportation placed a 1.5-in. thick
Type 8 binder course followed by a 1.5-in. thick Type 8 wearing
course. GlasGrid 8501 was placed between the two courses, with
one area left unreinforced to serve as a control section. The
6-year results of the monitoring undertaken post-rehabilitation
are presented in Figure 15 and clearly show the benefits of using
the GlasGrid System to retard reflective cracking.
IMAGE E: U.S. Highway 190, Hammond, LouisianaIMAGE D: U.S. Highway 96, Lumberton, Texas
U.S. Hwy. 96, Lumberton, TX
Percent Crack Reflection by Length
U.S. Hwy. 190, Hammond, LA
Percent Crack Reflection by Length
50
40
30
20
10
03 6 12 18 24 30 36 48 60 72
Time in Months
%C
rackingbyMeter
150
100
50
0
FIGURE 14 FIGURE 15
GlasGrid Longitudinal Cracks Control Longitudinal Cracks
GlasGrid Transverse Cracks Control Transverse Cracks
3 6 12 18 24 30 36 48 60 72
Time in Months
%C
rackingbyMeter
GlasGrid Longitudinal Cracks Control Longitudinal Cracks
GlasGrid Transverse Cracks Control Transverse Cracks
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STATE ROUTE 113, LORAIN COUNTY, OHIO
Located in Northeastern Ohio, Lorain County borders
Cuyahoga County and is approximately 30 miles west of
Cleveland (Image F). County growth, particularly in and
around the community of Amherst, brought increasing
traffic to local segments of State Route 113, a 60-mileeast-west highway that traverses four Ohio counties.
Recent measurements of AADT flow were recorded
at 13,400, primarily passenger automobiles.
To accommodate the growth in traffic, the Ohio Department
of Transportation (ODOT) District 3 authorized intersection
lane widenings along the route. Transportation officials,
who regard reflective cracking as a chief cause of pavement
distress, had not been satisfied with the results from standard
(unreinforced) methods of pavement widening and longitudinal
joint performance. In 2003, ODOT District 3 specified the use
of GlasGrid 8502 (or equivalent) at several designated
intersections, including one near the town of Elyria. There,
the GlasGrid System was placed directly over the longitudinal
widening joint and topped with two asphalt layers.
While the national average for reflection of unreinforced
longitudinal joints of this type is estimated to be approximately20% a year, the longitudinal joint reinforced with the GlasGrid
System reflected through at the much lower estimated rate
of 3% per year. The projected joint life for the reinforced joint
is 33.3 years; by contrast, the national average for similar
projects with unreinforced joints is projected to be just five
years. Field experience has demonstrated that the longer the
joint is protected, the longer the pavement service life, with
reduced life cycle costs such as crack sealing and pothole repair.
(Complete detail design information is available through Tensar.)
IMAGE F: State Route 113, Lorain County, Ohio
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AIRPORT APPLICATIONS
The GlasGrid Pavement Reinforcement System has been
used successfully on more than 100 airport projects over thepast 20 years. It has been particularly effective when installed
in airport runways, taxiways and aprons where transverse
thermal cracking or PCC joint cracking is prevalent on the
pavement surface.
In airport applications, the GlasGrid System is typically used
in one of two main ways:
Full width repairs of aged, random block cracked
or alligator cracked pavements that have not been
rehabilitated for many years GlasGrid 8501 or 8511.
Spot repairs applied over local transverse-cracked
areas GlasGrid 8502 or 8512.
INYOKERN AIRPORT, INYOKERN, CALIFORNIA
Inyokern Airport is located in the Indian Wells Valley, 80
miles from Palmdale, CA. Three large, paved runways can
accommodate almost any class of aircraft. Due to severe,
sudden daily temperature cycling, thermal stresses on the
airport pavements can be quite high, leading to serious
transverse cracking. Prior to undertaking rehabilitation,
large (1-1.5 in. wide), closely spaced, transverse cracks were
observed on the runway. It was decided that the intensity
of the cracking could negatively affect aircraft maneuvers
and safety.
The existing cracks on Runway 15-33 were first air-cleaned
and filled with a rubberized crack sealer. A -in. thick wearing
course was placed on top of the GlasGrid Mesh.
A site visit on January 31, 2007, showed that following 11 years of
service, the runway where the GlasGrid System was installed has
resulted in only minor cracking. In contrast, an area that was left
unreinforced for comparison purposes demonstrated significantly
more severe cracking up to 1-in. wide.
The airport general manager, Scott Seymour, recently stated,
Prior to the rehabilitation of Runway 15-33, we were dealing
with thermal transverse cracks ranging in width from 1-1.5 in.
wide. The use of the GlasGrid System in the rehabilitation
overlay has resulted in delaying the propagation of these
cracks significantly. Our experience with the GlasGrid System
has been very good and when a similar need arises in the
future, we will certainly consider the use of this product again.
Proven Performance
IMAGE G: Inyokern Airport used the GlasGrid System to rehabilitate Runway 15-33.
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GREATER ROCHESTER INTERNATIONAL AIRPORT
ROCHESTER, NEW YORK
The County of Monroe operates the Greater Rochester
International Airport as a medium hub for 16 air transportation
providers. It handles 220 flights a day to cities in the Northeast
and major hubs in the Midwest. In 1995, the airport authoritybegan investigating options for using interlayers to improve
the condition and performance of its secondary-use runway
for better overall performance.
The GlasGrid Pavement Reinforcement System was recom-
mended as a lower cost, longer lasting alternative to a thicker
asphalt overlay. Spot reinforcement of transverse cracks using
the GlasGrid 8502 product would provide a strong interlayer
solution capable of resisting the migration of reflective cracking.
A follow-up report from the Monroe County of Aviation indicated
that the GlasGrid Pavement Reinforcement System is delivering
very good performance after more than 11 years of service.
HECTOR INTERNATIONAL AIRPORT
FARGO, NORTH DAKOTA
The Municipal Airport Authority operates Hector International
Airport as a connecting hub for flights throughout the Midwest,
West and South. In 1996, the Airport Authority investigated
options for using high-strength interlayer mesh to prolong thepavement life of its main runway. Runway 13-31 is exposed to
harsh conditions on a year-round basis. With the average high
temperature being 82F in July and the average high temperature
being 16F in January, wide temperature swings, severe weather
conditions and heavy aircraft loadings were taking a toll on
the runway.
A follow-up distress survey indicated the GlasGrid Pavement
Reinforcement System is delivering very good performance
after more than 10 years of service with only minor cracking in
the high wheel loading areas. In contrast, the areas reinforced
with paving fabric are delivering only good performance
even though these sections of the runway experience much
less load and wear.
IMAGE H: Centralia Airport, Ontario, Canada condition of therunway before implementing the GlasGrid System.
IMAGE I:Condition of the Centralia runway 13 years afterinstallation of the GlasGrid System.
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6
GlasGridSystem Applications for Reflective Cracking
BLOCK CRACKSThe GlasGrid System should be specified when:
The unreinforced overlay design exceeds five years.
The average crack width is no greater than 1 in. (25 mm).
The block size is less than 10 ft x 10 ft (3 m x 3 m).
The minimum block size allowed is 1 ft x 1 ft (0.3 m x 0.3 m).
THERMAL CRACKS
The GlasGrid System should be specified for composite
pavements when:
The Load Transfer Efficiency (based on FWD results)
exceeds 70%.
The appropriate binder type has been selected for t he
project.
The correct grid st rength has been selected for the local
climatic conditions.
NOTE:Rate crack at highest severity level presentfor 10% or more of total crack length.
12 in. (0.3 m)
12 in. (0.3 m)
10 ft(3 m)
10 ft(3 m)
Traffic
CL
0.5 in. (12 mm)Medium severity
0.125 in. (4 mm)Low severity
0.75 in. (20 mm)
0.125 in. (4 mm)
Traffic
CONCRETE PAVEMENT JOINT CRACKS
The GlasGrid System should be specified when: The Load Transfer Efficiency (base on FWD results)
exceeds 70%.
The thermal cracking criteria are satisfied.
LANE WIDENING CRACKS
The GlasGrid System should be specified when:
The crack does not fall within the wheel path.
A level-up asphalt course should be specif ied when:
The subgrade t90
(time to achieve 90 % consolidation)
exceeds six months.
The new profile differs from the existing
(i.e., flexible vs. rigid).
Traffic
Jointreflective
crack
Jointreflective
crack
Transversecrack
Joint Original JCP Joint
Transversecrack
Transversereflected
crack
Longitudinal JointReflective Crack
2.5 ft(0.75 m)
2.5 ft(0.75 m)
GlasGrid 8502
2 in.(50 mm)Typicaloverlay
Existing pavement Additional lane widening
CROSS SECTION
PLAN VIEW
PLAN VIEW
AC overlay
PLAN VIEW
60 in. (1.5 m) wide GlasGrid 8502
2 in. (50 mm)
Asphalt binder course
Existing 2 in. (50 mm)binder course Aggregatebase course
Existing 2 in. (50 mm)
wearing course
Existing aggregate
base course
The four primary types of reflective cracks are:
Block Cracks
Thermal Cracks
Concrete Pavement Joint Cracks
Lane Widening Cracks
CL
High severity
CL
SHOULDER
SHOULDER
SHOULDER
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The GlasGrid System features a variety of products that
ensure optimum reinforcement benefits as the product is
matched to the specific needs and material characteristics
of a project. The most important considerations when selecting
a product are:
Aperture Size Needs to be matched to the grading
of the asphalt being reinforced. For asphalt mixes with
a maximum particle size less than -in., a product with
a standard sized aperture is appropriate. For coarser
mixes, a larger aperture grid should be used. The aperture
size may also be selected based on local environmental
conditions, mix stability, past performance or user
preference.
Tensile Strength The required tensile strength of a
pavement reinforcement grid is essentially determined
by the magnitude and activity of the existing cracks and
the traffic volume likely to be encountered. The greater
the amount of cracking or trafficking, the greater the
required tensile strength.
Grid Coverage The amount of grid coverage required is
determined by the type of crack pattern to be treated. For
discrete cracks such as those associated with construction
joints, it is possible to adopt a limited-coverage approach.
For areas that have or are likely to experience widespread
cracking, full-width and length coverage of the road
surface is typically recommended. The minimum
thickness of the asphalt overlay should be 1.5-in.
Moisture Barrier Some pavement engineers
maintain that significant long-term benefits are
obtained by providing a moisture barrier as well as
asphalt reinforcement. GlasGrid CG products help
provide a barrier by incorporating a lightweight,
polypropylene fabric on the back of the main grid
component. Upon placement, the tack coat seeps
into the fabric, forming a moisture barrier.
In most circumstances, a good quality moisture barrier can
also be produced using an open grid product. In this case,
the tack coat used routinely as part of the normal installation
procedure acts as an efficient moisture barrier. Open aperture
products also facilitate through-hole bonding and thereforeprovide a more effective means of reinforcing an asphalt
overlay. Consequently, although individual pavement engineers
may prefer to use a composite grid (incorporating a grid and
a fabric), generally speaking, an open grid product has proven
to yield significantly greater performance benefits. Table 4
on page 18 highlights the features and general uses of
various GlasGrid System products. Table 5 details their
specific applications.
Product Application Guide
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8
This chart outlines the main distinguishing features of the various GlasGrid
System products along with the specific applications for which they are
intended to be used.
Suggested Product Application
Installation Grid Coverage Asphalt Grading
GlasGridProduct
ApertureDimensions,
in. (mm)
TensileStrength,
AcrossWidth x Along
Lengthlbs/in.(kN/m)
Bonded toroad by
self-adhesivebacking on
the grid
Tack coatrequired tobond road
with the fabricbacking on
the grid
Full-widthcoverage fortreatment
of generallycracked road
surface
Discreetcoverage fortreatmentof specific
cracks
Less than in.
(19 mm)
Greater thanor equalto in.(19 mm)
Moisturebarrier is
the primaryfunction orpavement
is watersensitive
85010.5 x 0.5
(12.5 x 12.5)
560 x 560
(100 x 100)
85020.5 x 0.5
(12.5 x 12.5)
1,120 x 560
(200 x 100)
85111.0 x 1.0
(25 x 25)
560 x 560
(100 x 100)
85121.0 x .75
(25 x 19)
1,120 x 560
(200 x 100)
85501.0 x 1.0
(25 x 25)
280 x 280
(50 x 50)
CG501.0 x 1.0
(25 x 25)
280 x 280
(50 x 50)
CG1001.0 x 1.0
(25 x 25)
560 x 560
(100 x 100)
Based on environmental conditions, mix stability or past performance
Applicable under normal conditions
LEGEND:
(1) Fabrics cannot be used for these applications
(2) PCC joints must also be evaluated see (4)
(3) Crack sealing is recommended or mix ALD < crack width
(4) Load Transfer Efficiency must be greater than 70%, or ensure
that slab lengths are less than 20 feet.
(5) Effective for crack widths less than one inch.
(6) Interlayers not recommended for faulting joints
(7) Unreinforced overlay life must exceed five (5) years
(8) Ideally locate the LWJ outside the wheel path
(9) In poor subgrade zones, only low creep geogrids may be used
(10) Ensure that alligator blocks are stable under foot
(11) Potholes must be patched
(12) Check that surface drainage is functional
AADT= Average Annual Daily Traffic
PCC= Portland Cement Concrete
CTB= Cement Treated Base
SR= State Road
SH= State Highway
LWJ= Lane Widening Joint
TABLE 4: Product Features and General Uses of GlasGrid System
TABLE 5:Applications for the GlasGrid System
Primary/Critical Crack Type (Notes)
RoadType Traffic(AADT) Thermal(1,2,3,4,5,6) PCC Joints(3,4,5,6) Block(5,7,11)
Lane
Widening(1,7,8,9)
Alligator(7,10,11,12) CTB Shrinkage(1,5,7)
Moisture
SensitivePavement
Residential orparking area
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Specifications for Use in Asphalt Reinforcement
Property Test Method 8501 8511
Metric* Imperial** Metric* Imperial**
Tensile StrengthAcross Width
Across Length
ASTM D 6637 100 kN/m100 kN/m
560 lbs/in.560 lbs/in.
100 kN/m100 kN/m
560 lbs/in.560 lbs/in.
Elongation at Break ASTM D 6637 < 3% < 3% < 3% < 3%
Melting Point ASTM D 276 > 218C > 425F > 218C > 425F
Mass/Unit Area ASTM D 5261-92 370 g/m2 11 oz/yd2 370 g/m2 11 oz/yd2
Roll Length 100 m 327 ft 100 m 327 ft
Roll Width 1.5 m 5 ft 1.5 m 5 ft
Roll Area 150 m2 180 yd2 150 m2 180 yd2
Aperture Size 12.5 mm x 12.5 mm 0.5 In. x 0.5 in. 25 mm x 25 mm 1 in. x 1 in.
Adhesive Backing Pressure Sensitive Pressure Sensitive
Composition Custom-knitted fiberglass mesh with elastomeric polymer coating
and pressure sensitive adhesive backing.
TABLE 6
Detail RepairSystem
GlasGrid 8502 and 8512
PavementReinforcement Mesh
GlasGrid 8550
Complete RoadSystem
GlasGrid 8501 and 8511
TABLE 7
Specifications for Use in Asphalt Reinforcement
Property Test Method 8502 8512
Metric* Imperial** Metric* Imperial**
Tensile Strength
Across Width
Across Length
ASTM D 6637
200 kN/m100 kN/m
1120 lbs/in.560 lbs/in.
200 kN/m100 kN/m
1120 lbs/in.560 lbs/in.
Elongation at Break ASTM D 6637 < 3% < 3% < 3% < 3%
Melting Point ASTM D 276 > 218C > 425F > 218C > 425F
Mass/Unit Area ASTM D 5261-92 560 g/m2 16 oz/yd2 560 g/m2 16 oz/yd2
Roll Length 60 m 197 ft 60 m 197 ft
Roll Width
1.5 m 5 ft 1.5 m 5 ftRoll Area 90 m2 108 yd2 90 m2 108 yd2
Aperture Size 12.5 mm x 12.5 mm 0.5 In. x 0.5 In. 25 mm x 19 mm 1 In. x .75 In.
Adhesive Backing Pressure Sensitive Pressure Sensitive
CompositionCustom-knitted fiberglass mesh with elastomeric polymer coating
and pressure sensitive adhesive backing.
Product is sold by the roll.
*All metric values are nominal.
**All imperial values are approximate.
TABLE 8
Specifications for Use in Asphalt Reinforcement
Property Test Method 8550
Metric* Imperial**
Tensile Strength
Across Width
Across Length
ASTM D 663750 kN/m50 kN/m
(Across width)(Across length)
280 lbs/in.280 lbs/in.
Elongation at Break ASTM D 6637 < 3% < 3%
Melting Point ASTM D 276 > 218C > 425F
Mass/Unit Area ASTM D 5261-92 185 g/m2 5.5 oz/yd2
Roll Length 150 m 492 ft
Roll Width 1.5 m 5 ft
Roll Area 225 m2 269 yd2
Aperture Size 25 mm x 25 mm 1 in. x 1 in.
Adhesive Backing Pressure Sensitive
CompositionCustom-knitted fiberglass mesh with elastomeric polymer coating
and pressure sensitive adhesive backing.
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0
PAVEMENT PREPARATION
The key elements to consider when preparing a pavement for
the placement of GlasGrid products are: The existing pavement should be clean and dry, with
an even surface.
Any cracks exceeding 0.25-in. (6 mm) in width should
be sealed using an approved sealant or the appropriate
leveling course mix.
A minimum 0.75-in. (19 mm) thick asphalt concrete
leveling course should be placed.
Before laying the grid, the surface temperature should
be between 40F (5C) and 140F (60C).
Before placing GlasGrid products, the leveling course
should provide sufficient adhesion to the grid. A test
procedure for determining whether sufficient adhesion
exists is described below.
The minimum thickness of the wearing course should
be 1.5 in.
ADHESION TEST
The following procedure can be used to determine whether
sufficient adhesion exists between the GlasGrid and theunderlying asphalt:
Cut a square-shaped sample of the GlasGrid material
approximately one square yard in size.
Place the sample on the road surface to be paved.
Apply adequate vertical pressure to fully activate the
pressure sensitive adhesive e.g., by use of a rubber tired
roller or by other means.
Insert the hook of a spring balance under the center
of the GlasGrid sample (Image J).
Pull the spring balance upward until the sample starts
to pull loose, and record the gauge reading.
In the event that 20 lbs (19 kg) or more force is required
to pull the sample up from the road surface, sufficient
adhesion has taken place, and the paving operation
can begin.
In the event that the sample does not have sufficient
adherence, identify the cleanliness or moisture issues
present and resolve them before installing the rest
of the GlasGrid material.
Installation Procedures
IMAGE J:Testing GlasGrid for adhesion to underlying asphalt
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TACK COATS
A tack coat is a light coating of liquid asphalt applied either to
an existing pavement surface or on top of the installed GlasGrid
material. It is used to bond a new asphalt concrete course to the
existing pavement surface.
When the GlasGrid System was first introduced, tack coats werenot universally used on new leveling courses. More recently
however, the pavement industry has been implementing changes
to asphalt mixes in order to make them leaner, stiffer and more
rut-resistant. Consequently, these changes and the need to
maximize the bond between lifts have resulted in most authorities
mandating the use of a tack coat between all lifts of asphalt.
The GlasGrid System does not require a tack coat for installation.
However, when a tack coat has been specified for other reasons,
it should be used in accordance with the following guidelines*:
Type 1 NTSS-1HM, anionic, trackless tack. The trackless
tack is not sticky when cured, reducing the possibility of
pickup or build-up on paving equipment.
Type 2 Cationic, rapid set, CRS-2P. In general, cationic
emulsions can break and set more quickly than anionic
emulsions due to the electrochemical reaction between
the aggregate and the binder.
Type 3 Hot spray AC AC20-5TR-PG64-XX. In general,
hot spray AC tacks work well in cooler weather, whensurface temperatures are at or below 80F. When surface
temperatures exceed 80F, the manufacturer recommends
that an emulsion be applied in place of the hot spray AC.
Emulsions used with the GlasGrid System must break and
then cure before any additional asphalt is placed. Breaking is
defined as the point at which the brown colored fluid turns
black. Curing occurs when the residual asphalt cement contains
no solvents (water or any volatiles). Reference should be made
to the GlasGrid Installation Guide for additional information.
*Use of a tack coat type other than those specified above is notrecommended and will require a change in the application rule,a curing time and on-site supervision by the specifying engineer.
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2
Longitudinal joint
12" overlap
Transverse joints
36" overlap
GLASGRID PLACEMENT
There are two primary ways that the GlasGrid System can be
placed on an asphalt surface. The first, and more commonapproach, involves mechanical placement, typically with a
tractor that has been modified so that the GlasGrid material
can be front-mounted (Image K). The tractor is typically used
for full-width installations but can also be used for detail
repairs that are sufficiently large.
An alternative installation method involves manual placement
of the grid (Image L). Although the product is physically placed
by hand, it is highly recommended that the GlasGrid roll be
mounted on the back of a truck or other vehicle to help
maintain tension during placement. Manual installation
is more commonly used for localized areas of road.
Whether the GlasGrid System is placed mechanically ormanually, there are several general requirements to consider:
The grid must be installed under sufficient tension to
reduce or eliminate any ripples. If ripples do occur, they
must be removed prior to paving by pulling the grid
tight. In some cases (e.g., on curves with tight radii),
it may be necessary to cut the grid in short sections
(Figure 16).
Transverse joints should be overlapped in the direction
of the paver by three to six inches (75 to 150 mm);
longitudinal joints should be overlapped by one to two
inches (25 to 50 mm). The overlapping of two lengths
of GlasGrid is shown photographed in Image M and
diagrammatically in Figure 17.
In order to engage the pressure-activated adhesive, the
surface of the grid must be rolled with a rubber-coated
roller or pneumatic-tired roller. The tires must be kept
clean to avoid picking up the GlasGrid material during
installation.
Construction and emergency traffic may travel over the
GlasGrid material once it has been placed and rolled, but
turning and/or braking must be avoided at all times. Any
damaged sections caused by construction traffic must
be removed and patched prior to paving. It is alsoimportant that the GlasGrid System be kept free of
mud, dust and other debris during construction.
GLASGRID STORAGE
The GlasGrid System should be stored in a dry environment and
must not be exposed to excessive heat, moisture or ultraviolet
light. It should be kept covered and free from dust and dirt.
FIGURE 16: Cutting andoverlapping GlasGrid
around a curve
FIGURE 17: OverlappingGlasGrid across transverse
or longitudinal joint
IMAGE K: Mechanical placement of the GlasGridSystem.
IMAGE L: Manual placement of the GlasGridSystem.
IMAGE M: Overlapping the GlasGrid Systemacross transverse or longitudinal joint.
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Installation of the GlasGrid System is relatively simple and
straightforward. However, like all construction procedures,
there are advantages to using experienced personnel. This is
particularly true with the GlasGrid System since time is often
critical and the installation team must work quickly enough
to keep ahead of the paving machine.
Most authorized distributors are equipped to provide a full
installation service for the GlasGrid products they supply.
Installation rates are very reasonable and since modified
equipment is required for a mechanical installation procedure,
contracting these services is typically the easiest and most
cost-effective method for installing the GlasGrid System.
For additional information, check with your local GlasGrid
Distributor.
With thousands of successful installations worldwide, the
GlasGrid System can reduce maintenance costs and extend
pavement life on your highway, roadway, runway or parking
lot projects.
For more information on the GlasGrid Pavement Reinforcement
System, please call 800-TENSAR-1, visit www.tensarcorp.com
or [email protected]. We are happy to provide
additional GlasGrid System information, complete installation
guidelines, system specifications, design details, conceptual
designs, preliminary cost estimates, case studies, software
and much more.
Installation Services
GlasGrid is manufactured at an ISO 9001:2008 registeredfacility of Saint-Gobain ADFORS. GlasGrid is a registeredtrademark of Saint-Gobain ADFORS. U.S. Patent 5393559.Canadian Patent 1240873. European Patents WO2009/021040, WO 2009/021046, WO 2009/021051.
Japanese Pa tent 261 1064. Ad ditional pat ents pendin g.GlasPave 25 is designed to meet ASTM D7239, HybridGeosynthetic Paving Mat for Highway Applications Type 1.GlasPave 50 is designed to meet ASTM D7239, HybridGeosynthetic Paving Mat for Highway Applications Type 1.
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asGrid is the registered trademark of Saint-Gobain ADFORS and GlasPave is a trademark of Saint-Gobain ADFORS. GlasGrid and GlasPave are distributed in the United Statesf America, Canada and certain other countries by Tensar International Corporation (Tensar). Inasmuch as Saint-Gobain ADFORS and Tensar have no control over installation design,stallation workmanship, accessory materials, or conditions of application, Saint-Gobain ADFORS and Tensar do not warrant the performance or results of any installation or use ofasGrid. This warranty disclaimer includes all implied warranties, statutory or otherwise, including the warranty of merchantability and of fitness for a particular purpose. The values
nd tolerances given are obtained in our laboratories and in accredited testing institutions All imperial values are approximate The information given in this data sheet is to the best
Distributed by:
Exclusive distributor inthe Americas for:
Tensar International Corporation
2500 Northwinds Parkway, Suite 500
Alpharetta, Georgia 30009
800-TENSAR-1
tensarcorp.com